The present invention relates to a novel method for producing hollow rayon fibers, which are light and heat-insulating, in a simple and environmentally friendly manner.
Rayon fibers, which are artificial fibers with the same chemical structure as cellulose, are defined as regenerated cellulose fibers, in which 15% or fewer hydroxyl groups are substituted (Fibers Chemistry, Manachem Lewin Eli M. Pearce, Dekker p.914, 1985), and usually used in high-grade applications with favorable intrinsic brightness, specific gravity, and sense of touch.
Viscose rayon (hereafter, referred to simply as xe2x80x98rayonxe2x80x99) can be produced by spinning a sodium cellulose xanthate solution, prepared by adding a sodium hydroxide solution and CS2 to cellulose, into an aqueous solution of sulfuric acid and zinc sulfate. Such method was commercialized, but recent legislation, in response to environmental concerns stemming from air pollution, has been enacted to make the method useless because it produces harmful substances such as CS2.
Therefore, it is an object of the present invention to provide a commercial method for producing hollow rayon fibers, which are light and heat-insulating, in a simple and safe manner.
To accomplish the above object, the present invention provides a method for producing hollow rayon fibers, which comprises the steps of saponifying cellulose acetate fibers with a degree of acetyl substitution of 2.0 to 3.0 (acetification of 45 to 62.5%) by use of an aqueous solution of strong and weak alkali in such a way as to substitute 27 to 75% of the total acetyl groups of cellulose acetate fibers with hydroxyl groups in order to form a cellulose layer with a mixed crystalline structure of cellulose II and TV; followed by dissolving a cellulose acetate portion which is not saponified by use of an organic solvent.